Time out should be administered on an individual basis.  Each child reacts differently to it therefore, an alteration could be considered.  One child my do well with one minute for each year of their life, others will not.

A secondary method used by this webmaster and others successfully for their defiant child, has been this:
 

Child's Reaction:

Alteration:

The first offence:   The child defies or otherwise acts up:             The child continues to act up, or further defiance is exhibited:     If defiance or disruption continues:

The  child is placed in time-out for a five minute period. Take the steps of 'Warning' the child of additional time.  If warning is heeded within 5 seconds, continue with present time. If child does not heed the warning, one minute is added to the overall time making the time now 6 minutes. Another warning is given and the 5 second rule is followed.  If compliance is found continue with the present time.  If not, add one more minute to the overall time Minutes are added for each offence.

For the second, third, and fourth, etc. occurances in a day the starting time will have another five minutes added to the time-out.  The starting time is ass follows:

During these time-out occurances, if defiance and disruption is still occuring, the additional minutes are added.

Also, it is not good that this be carried into extended periods of time.  Preferably, no more than 30-45 minutes depending on the severety of the defiance and oppositional traits exhibited by the child.

This method will take several times for the child to see that it is going to be consistent.  Once the child realizes that the teacher is indeed consistent, they will quickly alter their behavior accordingly to avoid the additional time.